Chemical composition, structures, and light absorption of N-containing aromatic compounds emitted from burning wood and charcoal in household cookstoves

Abstract

N-containing aromatic compounds (NACs) are an important group of light-absorbing molecules in the atmosphere. They are often observed in combustion emissions, but their chemical formulas and structural characteristics remain uncertain. In this study, red oakwood and charcoal fuels were burned in cookstoves using the standard water-boiling test (WBT) procedure. Submicron aerosol particles in the cookstove emissions were collected using quartz (Qf) and polytetrafluoroethylene (PTFE) filter membranes positioned in parallel. A backup quartz filter (Qb) was also installed downstream of the PTFE filter to evaluate the effect of sampling artifacts on NAC measurements. Liquid chromatography–mass spectroscopy (LC–MS) techniques identified 17 NAC chemical formulas in the cookstove emissions. The average concentrations of total NACs in Qb samples (0.37±0.31–1.79±0.77 µg m−3) were greater than 50 % of those observed in the Qf samples (0.51±0.43–3.91±2.06 µg m−3), and the Qb-to-Qf mass ratios of individual NACs had a range of 0.02–2.71, indicating that the identified NACs might have substantial fractions remaining in the gas phase. In comparison to other sources, cookstove emissions from red oak or charcoal fuels did not exhibit unique NAC structural features but had distinct NAC composition. However, before identifying NAC sources by combining their structural and compositional information, the gas-particle partitioning behaviors of NACs should be further investigated. The average contributions of total NACs to the light absorption of organic matter at λ=365 nm (1.10 %–2.57 %) in Qf and Qb samples (10.7 %–21.0 %) are up to 10 times larger than their mass contributions (Qf: 0.31 %–1.01 %; Qb: 1.08 %–3.31 %), so the identified NACs are mostly strong light absorbers. To explain more sample extract absorption, future research is needed to understand the chemical and optical properties of high-molecular-weight (e.g., molecular weight, MW>500 Da) entities in particulate matter.